1. Field of the Invention
The present invention relates to a zoom lens system and more particularly to a zoom lens system applicable to a video camera or a still video camera.
2. Description of the Prior Art
Recently, since the compactness of a plurality of electric circuits and integrated circuits contained in a video camera system and the like are improved, the lens system contained in such a camera system possesses a large proportion of the size and weight of the entire camera system. The cost of the lens system is also large enough to prevent the cost of the whole camera system from being lowered. The compactness in size, the lightness in weight and the low cost are indispensable for such video camera systems. Therefore, how to construct the lens system as compact in size, light in weight, and low in cost as possible is an important matter.
A solution of the above matter often results in abandoning the use of the zoom lens system and adopting a fixed focal length lens system. Though the adoption of the fixed focal length lens system realizes the compactness in size, the lightness in weight and the low cost of the whole camera system, the charm is much reduced because of the fixed focal length thereof. The focal length of a lens system can be altered by attaching a converter or an attachment thereto. However, such convertor or attachment should be carried separately from the camera body. Additionally, it is hard to be certain that the smaller size, lighter weight and lower cost have been realized, if the converter or attachment is included in the entire system. Also, in recent years, a lens shutter camera including a converter has been proposed so that the converter can be inserted to or retracted from a photographing path to convert the compound focal length of its photographing lens system. However, it is also hard to be certain that such lens shutter camera realizes the smaller size, lighter weight and lower cost. Additionally, since the zoom ratio realized by such lens shutter camera is relatively as small as 2.0 and it is impossible to change the compound focal length with continuing photographing operations, the charm is also much reduced.
Then, a zoom lens system is considered to be applied again. However, most conventional zoom lens systems are designed to achieve a high zoom ratio, and therefore are large in size and very expensive. To the contrary, Japanese Laid-Open Patent Application No. 143311/1986 proposed a zoom lens system designed to realize the compactness in size, light in weight and low in cost with a low zoom ratio, but such a proposed zoom lens system can not be put in practical use because of its insufficient correction of aberrations, particular of the chromatic aberration.